In 1696, the most famous scientist in England retired from physics. Isaac Newton spent the next thirty years working undercover in London taverns, alleys, and prisons to hunt counterfeiters. He sent at least twenty-eight men to be hanged, drawn, and quartered.

Newton was fifty-three. He had finished the Principia, the calculus, and the optics. He had, by his own private account, finished with science. He needed an income. The Royal Mint at the Tower of London needed a Warden. A friend at the Treasury arranged the appointment. Most Wardens regarded the post as a sinecure. Newton did not. He arrived at the Tower on the third of May, 1696, and he took the office as if it were a war.

About one in ten coins in English circulation was counterfeit, mostly clipped silver and forged guineas. Newton interrogated suspects himself in cells at Newgate Prison. He recruited informants in London brothels and gambling dens. He went out at night, in a dark cloak, with a leather notebook, to collect evidence in person. He composed indictments by hand. He cross-examined witnesses more than one hundred times in two years. He prosecuted cases at the Old Bailey. He sent twenty-eight men to the scaffold at Tyburn, where they were hanged, drawn, and quartered, the punishment for high treason. He kept the case files in his own desk.

His greatest target was a brilliant Warwickshire-born counterfeiter named William Chaloner, who had grown so rich he owned a house in Knightsbridge. Chaloner attacked Newton publicly in printed pamphlets and tried to have him dismissed from the Mint by petitioning Parliament. Newton's response was to build the case for Chaloner's execution patiently over three years. Chaloner was hanged at Tyburn on the twenty-second of March, 1699. He wrote begging letters to Newton from the condemned cell at Newgate. Newton did not reply. Newton was promoted to Master of the Mint that same year. He died in office in 1727, aged eighty-four. His statue at Westminster Abbey shows him with a book and a celestial globe. Not with a noose.

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